Open Windows Explorer by pressing Windows flag button + E (the button in between left Ctrl and Alt), or go to My Computer on the desktop.

Since I have no idea where you installed the game, and you neither, I suggest to right-click on My Computer and choose Search.

In the search fields you can specify your search, and type in a name or a wild card, etc.

I suspect you chose the standard path for the game to install, so there's a good chance it will be on C:\ .

Type in Medieval and wait for the search to finish. After a little while the folder should be found. Then just click and click until you get to it.